MORPHOLOGY:
The nasal bones of the pig-tailed langur are elongated and the nose is snubbed. The average body mass for an adult male pig-tailed langur is around 8.7 kilograms, and it is around 7.1 kilograms for females. The hindlimbs and forelimbs of this species are equal in length (Ankel-Simons, 2000). This species is sexually dimorphic in terms of body size and canine size (Tenaza and Fuentes, 1995). This species is asexually dichromatic, meaning any sex can be of one of two color types (Tilson, 1977). The two color types are a dark gray color and a light buff color (Tilson, 1977). The face of this species is black in color (Ankel-Simons, 2000). This species has a relatively short tail for colobines and the tail is hairless (Watanabe, 1981). This species shows a preference for what hand it uses during feeding and support (Miller and Paciulli, 1998).

RANGE:
The pig-tailed langur is found on the Mentawai Islands which are off of the west coast of Sumatra. The four main islands consist of Siberut, Sipora, North Pagai, and South Pagai. This species lives in primary forests on hillsides of the interior region of the islands (Tilson, 1977). The pig-tailed langur also lives in fresh-water and brackish-water swamp forest and lowland rainforest (Tenaza, 1989b).

ECOLOGY:
The pig-tailed langur is primarily a folivorous species, but also consumes fruits and berries. On the island of Simalegu this species consumes most frequently the species nibung, an inflorescence plant (Tenaza, 1987). When this species enters a food tree, it will forage in the more densely foliated part of the tree and feed quietly (Tilson, 1977). The pig-tailed langur has feeding peaks in the morning and in the late afternoon (Tilson, 1977). When feeding groups will break up and spread out over an area of up to 90 meters in diameter (Tenaza and Fuentes, 1995). Females with infants will park their infants in a tree crown while they feed (Fuentes and Tenaza, 1995). Infants will sometimes cry when placed in the crown of a tree while their mother forages (Fuentes and Tenaza, 1995). The advantages of infant parking are that a female might not have use as much energy when foraging if she would have to carry an infant, and a female might be better able to flee from predators if not having to carry an infant around (Fuentes and Tenaza, 1995). The pig-tailed langur has a preference to feed with the right hand when the non-feeding hand is not engaged in any activity (Miller and Paciulli, 1998).

Group sizes for this species, on the islands of Simalegu and Sinaka, range from 1 to 5 individuals (Tenaza, 1987). The pig-tailed langur is a diurnal and semi-terrestrial species. This species sleeps in the densely foliated emergent trees found on hillsides (Tilson, 1977). This species was also found to sleep in densely foliated trees in the secondary layer of the canopy (Kawamura and Megantara, 1986). Group travel is lead by either sex (Tenaza and Fuentes, 1995).

To avoid predators, mostly humans, this species will remain motionless in dense foliage, not making a sound (Tilson, 1977). The pig-tailed langur will also drop to the ground and try to flee (Tilson, 1977).

LOCOMOTION:
The pig-tailed langur moves through the forest and on land quadrupedally (Fleagle, 1988).

SOCIAL BEHAVIOR:
The pig-tailed langur has a monogamous or polygynous mating system. Tenaza and Fuentes (1995) suggest that the mating system of this species be called monandry, which they define as "a mating system in which the breeding group consists of 1 adult male and greater than or equal to 1 adult females plus their young, such that the population of breeding groups consists of a mixture of monogamous and polygynous families." In areas of high densities groups of this species tend to be polygynous (Cheney and Wrangham, 1987). Watanabe (1981) has suggested that predation, by humans, may force monogamy for the pig-tailed langur. In Northern Siberut Island this species tends to be polygynous, whereas in the rest of the island it is monogamous (Watanabe, 1981). Males not found in groups will live solitarily and occupy a territory (Tenaza and Fuentes, 1995). When two group males visualize each other they will rapidly approach one another, then stop at about 25 meters (Tilson, 1977). Then one male will elicit the loud call with the other reciprocating before both males run back to their respective groups and fleeing into their home range (Tilson, 1977). The home ranges of group tend to overlap a little (Tenaza and Fuentes, 1995).

VOCAL COMMUNICATION:loud call: This call consists of a series of 2 to 25 nasal barks and travel about 500 meters in the forest. The first barks of this call are the loudest with subsequent calls decreasing in volume with the last barks being faint (Tenaza, 1989b). These loudest barks are followed by audible gasps (Tenaza, 1989b). The mean duration of this call is 12.1 seconds (Tenaza, 1989b). These calls are mostly made during the morning and late afternoon. These are used to maintain distance between groups and to bring the group together. There are peak times when this call is emitted, in the morning and in late afternoon (Tenaza, 1989b). This call is also heard as a response to thunder and falling trees (Tenaza, 1989b).

OLFACTORY COMMUNICATION:

VISUAL COMMUNICATION:

TACTILE COMMUNICATION:social grooming: This is when one individual grooms another and is used to reinforce the bonds between individuals.

REPRODUCTION:
The pig-tailed langur gives birth to a single offspring. During estrus the anterior perineum of the female swells and turns a pink color (Tenaza, 1989a). The birth season for this species is from June to July (Tilson, 1977).